Chemical pollution in coastal areas is an important and increasing problem in Chile. Lenga's area is one of the most polluted zones in Chile. In order to develop a non destructive pollution instrument, samples of blood of catsharks Schroederichthys chilensis (Guichenot 1848) both from Dichato (control zone) and Lenga (problem zone) were obtained between September and October 2003 (20 individuals in each zone). The blood parasites Trypanosoma humboldti (Morillas et al. 1987) were determined in a Kova camera. The amount of trypanosomes in Lenga (5,7 trypanosomes/ml) was lesser than the control zone (9,1 trypanosomes/ml; p=0.0007). The eosinophills were also fewer in Lenga (6.494 cells/ml) than Dichato (8.226 cells/ml; p=0.027). We hypothesize that minor counts of trypanosomes in Lenga could be explained by the cell damage produced by chemical pollution. The standardization procedure done for the method to quantify trypanosomes allowed a very effective tool in order to identify zones with different grade of pollution and also serves for utilizing the Chilean catshark as bioindicator of chemical pollution without killing the fish